Oil well treatment to prevent coning



April 16, 1957 c. B. PETERSON OIL WELL TREATMENT TO PREVENT CONING Filed July 25, 1954 AV AV AV/AV/AV tatciS Unite OIL WELL TREATMENT TO PREVENT CONING Application July 23, 1954, Serial No. 445,254

6 Claims. (Cl. 16d42) This invention relates to the production of liquid petroleum hydrocarbons from a subsurface reservoir. More particularly, this invention relates to the production of liquid petroleum hydrocarbons from a subsurface reservoir which overlays a substantially water-saturated porous formation. Still more particularly, this invention relates to a method for overcoming water-caning which sometimes results during the production of liquid petroleum hydrocarbons from a liquid petroleum-producing formation which overlays a substantially Water-saturated formation.

Water-coning is a term given to the mechanism underlying the entry of bottom waters into oil-producing wells. Liquid petroleum hydrocarbons are often produced from porous subsurface formations which overlay a substantially water-saturated porous formation. Under the static conditions the water, being of greater density than the liquid petroleum, remains at the bottom of the liquid petroleum-producing formation. At high rates of production of liquid petroleum however, the upper surface of the substantially water-saturated formation rises due to the increased flow of liquid petroleum into the well bore which extends into the liquid petroleum-producing formation immediately adjacent and above the substantially water-saturated formation. The rise of water into the liquid petroleum-producing formation and into the well bore represents a dynamic elfect in which the upward directed pressure gradients associated with the flow of the liquid petroleum into the producing well bore are able to balance the hydrostatic head of the resulting elevated water column.

Various methods have been suggested heretofore to eliminate or to reduce the water-coning phenomenon. These methods have included reducing the Well penetration into the liquid petroleum-producing formation so that higher production rates are possible without at the same time experiencing a relatively increased production of water therewith. Another method which has been suggested is to bottom the producing well into a substantially water-impermeable formation. These indicated methods, however, cannot be successfully employed in all instances to eliminate or reduce water-caning. Certain underground liquid petroleum-producing formations are only a relatively few feet in thickness. Accordingly, reducing the well bore penetration into such a formation would unduly restrict the recovery of liquid petroleum therefrom. Other liquid petroleum formations do not have associated therewith an immediately underlying water-impermeable formation.

It is an object of this invention to provide an improved method for the recovery of liquid petroleum hydrocarbons.

- It is another object of this invention to provide an improved method for the recovery of liquid petroleum hydrocarbons from a liquid petroleum-producing formation which overlays a substantially water-saturated formation.

It is still another object of this invention to provide 2,788,855 Patented Apr. 16, 1957 ice a method of preventing and/ or reducing water-coning as evidenced by the production of a relatively large amount of water with respect to produced liquid petroleum during the production of liquid petroleum from a well bore extending into a liquid petroleum-producing formation and an adjacent underlying water-producing formation.

It is still another object of this invention to provide an improved method of well completion wherein the well bore extends into a liquid petroleum-producing formation which overlays a water-producing formation.

These and other objects of this invention and how they are accomplished will become apparent with reference to the accompanying drawing wherein:

Fig. 1 schematically illustrates the water-caning phenomenon; and

Fig. 2 schematically illustrates a method in accordance with this invention for overcoming water-coming.

In accordance with this invention water-coning is overcome by injecting into the water-producing formation giving rise to the water-coming phenomenon a substantial amount of gas. As the gas is injected into the waterproducing formation, the water filling the pores or interstices .of the formation is displaced and forced back by the injected gas. The injection of gas into the waterproducing formation is continued until the water has been displaced a substantial radial distance, e. g., at least about 5 feet, preferably at least about 20 feet, from the point of injection, which is conveniently the well bore itself. Initially, the pores of the water-producing formation are usually substantially saturated with water, i. e., percent occupied by water. It is preferred in the practice of this invention to reduce the water content of the pores of the water-producing formation to the irreducible minimum for a substantial extent in the area surrounding the location of gas injection. Depending upon the geometrical configuration of the pores or interstices of the waterproducing formation the irreducible minimum water content is usually in the range 2-50 percent of the pore space.

Various gases may be employed in the practice of this invention. Suitable gases include natural gas, usually associated with and dissolved in the liquid petroleum-producing formation and which is recovered by suitable means, such as a gas-liquid separator at the surface. It is preferred that the injected natural gas be dry, that is, having had its natural gasoline content stripped therefrom. Another gas which may be employed in the practice of this invention is air. Still another gas which is suitable in the practice of this invention is a gaseous mixture of combustion products such as a line gas and the like, usually containing nitrogen, carbon dioxide, and other gases in varying amounts. It is possible in the practice of this invention to reduce the water content of the water-producing formation into which the gas is injected, to an amount below the irreducible minimum by injecting into the Water-producing formation a hot gas, such as hot combustion gases, so as to substantially dry the formation into which this gas is injected. In accordance with another aspect of this invention there is added to the injected gas a small amount of a vaporized material which deposits within the treated formation a film preferentially wettable by oil, e. g., a hydrophobic film. Suitable materials include the halo-silanes containing hydrocarbon groups such as the alkyl chloro-silaues including monornethyl dichloro-monosilane, dimethyl dichloro-monosilane, diethyl dichloro-monosilane, dipropyl dichloro-monosilane, dibutyl dichloro-monosilane, triethyl monochloro-monosilane and the like, which readily hydrolyze upon contact with water to form a hydrophobic film within the interstices of the formation. This hydrophobic, preferentially oil-wetted film further reduces the water-permeability of the formation wherein the gas is injected. Also suitable are the aryl and arallryl halosilanes.

Referring now to Fig. 1 of the drawing which schematically illustrates the water-coming phenomenon, a subsurface liquid petroleum-producing formation is indicated at 11 An immediately underlying, substantially saturated, water-producing formation is indicated at 12. A well bore 13 extends into the liquid petroleum-producing formation '11 and the water-producing formation 12. A production casing 14 is provided with perforations 15 within the petroleum-producing formation 11. Under static conditions or at a relatively low rate of liquid petroleum production from the liquid petroleum. formation 11, the upper surface of the water-producing'formation is located at about the position indicated by the dashed line 16. At relatively high rates of production,

however, because of the upwardrdirected pressure gradients associate'd with the flow of liquid petroleum into perforations 15, the water table rises to the extent it is balanced by these upward directed pressure gradients. As the water table rises, as indicated by solid line 17, to the area of production of liquid petroleum hydrocarbons, water is produced by the lowermost perforations 15 of casing it. At still greater rates of production of liquid petroleum from formation 11, the water table continues to rise and there results a greater production of Water relative to the amount of produced liquid hydrocarbons. The above-described phenomenon is commonly known as water-coi ing. 7

Referring now to Fig. 2 of the drawing, there is schematically illustrated therein a method according to this invention for preventing and/or reducing water-coming.

. The same reference numerals have been employed in Fig. 2 as were employed in Fig; 1 for reasons of clarity and ease of understanding, As indicated in Fig. 2, Well bore 13 provided with casing 14 extends into liquid petroleum-producing formation 11 which overlays water-producing formation 12. In order to prevent and/or reduce water-coming when the production of liquid petroleum is commenced by perforating casing 14 within the petroleum-producing formation 11, packing 18 is inserted within casing 14- at about the normal interface of the formations 11 and 12, as indicated by dashed line 16. After the packing 18 has been installed, a gas such as dry natural gas is injected via conduit 19 into the formation 12 via perforations 20 in the casing 14. The injection of gas into formation 12 is continued until the water has been displaced within formation 12 for a substantial radial distance surrounding that portion of well bore 13 within formation 12, to the extent indicated by t dashed line 21. After a sufficient amount of gas has been injected to displace the water from around the well bore 13 immediately adjacent the liquid petroleumproducing formation 11, the injection of gas is stopped and the production of liquid petroleum from formation 11 is com- I menced by perforating casing 14 within the formation 11 as indicated. As the liquid petroleum flows through perforations 15 into production casing 14, upward-directed pressure gradients are created which tend to lift the water table into the liquid, petroleum formation 11 in the area of the wellbore 13. Accordingly, the water present within the water-producing formation 12 tends to fill the spaces or pores of formation 12 from which it .was displaced by the injected gas. However, the fiowof water into and within the zone indicated by reference numeral 21 is resisted because of the reduced permeability ofthislocalized portion of formation 11 due to the presence of a substantialam'ount of gas present in the interstitial voids thereof. Due to the reduced permeability of zone 21 considerable resistance to the flow of water therethrough is experienced with the resultthat the rate of liquid petroleum production through perforations 15 can be greatly increased without experiencing an undue amount of produced water due to water-coming.

The practice of this invention is applicable not only to newly-drilled wells as indicated hereinabove but is also applicable to previously drilled wells which are producing a considerable amount of water due to the phenomenon of water-coning, In previously drilled producing wells which exhibit an unduly large amount of water production due to water-coning, the practice of this invention is as follows.

The liquid hydrocarbon-water producing well is 'shut in for a period of time necessary to establish equilibrium conditions in the subsurface producingformations. This period of time, depending upon various circumstances, may be three hours to a month. After equilibrium conditions have been'established, a' gas is injected into the duction casing in the water-producing Zone and injecting gas thereinto. After a sufiicient amount of gas has been injected to force the water in the formation a substantial radial distance outwardly from the well bore at the point 'of injection, gas injection is stopped and production commenced in the manner indicated with reference to Fig. 2.

The method of this invention is applicable not only to so-called gas-drive liquid petroleum reservoirs but also to so-called water-drive reservoirs. 7

As will be apparent to those skilled in the art, many substitutions, alterations or emissions are possible without departing rom the spirit or scope of this invention.

I claim: 7

1. A method of reducing water-coming, as evidenced 'by production of a relatively large amount of. water with respect to produced liquid petroleum, which is experienced during the production of liquid petroleum from a well bore extending into a subsurface liquid petroleum-producing formation and an adjacent underlying water-producing formation which comprises halting production of liquid petroleum from said well bore to promote the attainment of equilibrium conditions in the subsurface formations, then injecting via said well bore into said water-producing formation surrounding said well bore an amount of gas sufiicient to force the water in said waterproducing formation a substantial distance outwardly from said well bore and thereafter resuming production 7 of liquid petroleum from said liquid petroleum-producing formation via said well bore.

2. A method in accordance with claim 1 wherein the amount of gas injected is sufficient to reduce the water content of the water-producing formation to about. the irreducible minimum for a substantial distance outwardly from said well bore. I

3. A method in accordance with claim 1 wherein the gas is air.

4. A method in accordance with claim 1 wherein the gascomprises gaseous products of combustion.

5. A method in accordance with claim 1 wherein the gas injected comprises hot gaseous products of combustion in an amount suflicient to occupy substantially all of the available pore space in the water-producing formation for a substantial distance outwardly from said well bore.

6. A method in accordance with claim 1 wherein there is added to the injected gas an amount of a vaporous material which deposits a hydrophobic, preferentially oilwetted film within the intersticesof the formation wherein.

the gas is iniected.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF REDUCING WATER-CONING, AS EVIDENCED BY PRODUCTION OF A RELATIVELY LARGE AMOUNT OF WATER WITH RESPECT TO PRODUCED LIQUID PETROLEUM, WHICH IS EXPERIENCED DURING THE PRODUCTION OF LIQUID PETROLEUM FROM A WELL BORE EXTENDING INTO A SUBSURFACE LIQUID PETROLEUM-PRODUCING FORMATION AND AN ADJACENT UNDERLYING WATER-PRODUCING FORMATION WHICH COMPRISES HALTING PRODUCTION OF LIQUID PETROLEUM FROM SAID WELL BORE TO PROMOTE THE ATTAINMENT OF EQUILIBRIUM CONDITIONS IN THE SUBSURFACE FORMATIONS, THEN INJECTING VIA SAID WELL BORE INTO SAID WATER-PRODUCING FORMATION SURROUNDING SAID WELL BORE AN AMOUNT OF GAS SUFFICIENT TO FORCE THE WATER IN SAID WATERPRODUCING FORMATION A SUBSTANTIAL DISTANCE OUTWARDLY FROM SAID WELL BORE AND THEREAFTER RESUMING PRODUCTION OF LIQUID PETROLEUM FROM SAID LIQUID PETROLEUM-PRODUCING FORMATION VIA SAID WELL BORE. 